Like-for-like sales at market leader Tesco fell 0.9 per cent in the 12 weeks to Aug. 16, Kantar said, as strong growth in its convenience shops and online could not offset lower revenue at larger stores.LONDON: Britain's "big four" supermarkets have all lost market share in a barely growing grocery market, with Tesco and its main rivals failing to keep pace with discounters Aldi and Lidl, Kantar Worldpanel said on Tuesday.

German-owned Aldi and Lidl now have a combined market share of 9.7 per cent, versus 8.4 per cent a year ago, according to the market research company.

Like-for-like sales at market leader Tesco fell 0.9 per cent in the 12 weeks to Aug. 16, Kantar said, as strong growth in its convenience shops and online could not offset lower revenue at larger stores.

Asda, which this month said it had suffered its worst quarterly sales performance since it was bought by US group Wal-Mart 16 years ago, saw a 2.5 per cent decline and Morrisons was down 1.1 per cent.

Tesco's market share fell from 28.8 per cent to 28.3 per cent year on year, with Asda's share falling from 17.2 per cent to 16.6 per cent and Morrison's down slightly.

Sainsbury's, which vies with Asda for the second position, eked out a 0.1 per cent sales rise, Kantar said, but it was not enough to stop its share of the market falling 0.1 per centage points to 16.3 per cent.

Discounters Aldi and Lidl, whose cheap own-brand goods have forced Britain's big four to slash prices in an attempt to hold on to shoppers, both saw sales growth accelerate to 18 per cent and 12.8 per cent respectively.

Overall grocery sales grew 0.9 per cent, Kantar said, continuing a year-long trend of 1 per cent or less growth as record commodity-led deflation also pushes prices down.